Printed circuit borads (hereinafter boards) are the basic building blocks of any type of electronic product. Further, as can be noted with virtually any electronic product these products have been continually decreased in size without loss of any functions or with additional functions included. For example, in mobile applications, such as vehicle two way communication radios, the standard radio size has been 3 by 18 by 24 inches. These radios typically were accommodated in the dash, in the body, in the trunk, under the seat or in the floor board of the vehicles. The design criterion for newer radios now is on the order of 21/2 by 7 by 12 inches, which allows for installation under the dash of modern automobiles.
Therefore, there is a need to develop smaller components to be mounted on the boards and a way of mounting the components on the boards in the highest packing density possible without causing or increasing soldering defects.
One development in smaller size components is the leadless component. These components presently include resistors, capacitors, potentiometers, trimmers, inductors, diodes, transistors and integrated circuits and can include other electronic components. further, some of the components include both leadless and lead type terminals. The leadless components are mounted on at least the solder side of the boards and generally are electrically connected by a molten soft solder process such as wave soldering or dipping, if desired.
The leadless components, especially the capacitors and resistors, generally are formed with a ceramic or alumina substrate material which result in fragile components. This is not a problem in the soldering process and would not be a problem, if the boards were not subjected to various stresses. The boards, however, generally are subjected to external bending stresses which can place excessive loads on the components causing cracks or outright fractures in the components and hence defective boards.
The stresses on the components can be controlled by controlling the solder fillets which are formed in the soldering process. One prior technique involves limiting the solder area on the board at each terminal of the component. This can be effective in utilizing two terminal components, but does not provide for an increased packing density of the components on the boards without increasing soldering defects; such as by bridging between adjacent components or component leads.
It is therefore a general object of the present invention to provide a solder fillet control pattern which provides a predictable control of the component solder quality.
It is a further object of the present invention to provide fillet control boxes to define the individual component locations on the board.
It also is an object of the present invention to increase the packing density of the components mounted on the boards without increasing soldering defects.